1. Rural – land degradation in a semi-arid
Area.
STARTER – Write out the assessment specification below.
The impact and management of rural land degradation related to a rainforest or semi-arid area.

2. Course Outline
This section of the Rural course will look at land degradation in a semi-arid area:
Sahel region of Africa (developing country example)
Physical and Human causes of land degradation
Impact of soil degradation on the people and the landscape
Soil conservation methods in this region

3. Land Degradation – What is it?
Soil can take hundreds of years to form and, like much of the earths surface, is exposed to erosion. If the erosion of the soil happens faster than it is formed then we say that the soil is becoming degraded.
This can mean that the quality of the soil is diminished or that the top soil might be removed altogether.
As we try to produce more food for the growing population, or for profit, agricultural land is put under pressure and begins to fail. Developed countries can afford to use expensive solutions like fertilisers, but developing countries struggle to afford this.

4. Causes of land Degradation
Land degradation occurs because the vegetation cover is removed, by humans or animals, and the soil is exposed to wind and water erosion.

5. Soil Erosion by Water
Soil erosion by water can by summarised into 3 stages:
Detachment – soil particles become detached from main body of soil by individual raindrops hitting soil or overland flow
Transportation – soil particles carried downhill; floating, dragged or splashed.
Deposition – soil particles put down (river/ lake or sea-bed)

6. Soil Erosion by Water
There are four main types of soil erosion by water:
Rainsplash – concerned with the impact of raindrops on the surface of a soil.
Sheet wash – the removal of a thin, almost unseen, layer of surface soil.
Rill erosion – the creation of very small eroded channels across a soil surface
Gully erosion – creation of large gullies large quantities of water flowing over the soil surface.
Lets look at these in a little more detail.

7. Rainsplash Rain can splash soil up to 30cms.
The bigger the raindrop and the faster it fall the harder it hits the ground. These create an explosive impact; creating a mini crater by blasting soil particles outwards.
This loosens soil and breaks down the ‘crumb structure’ of the soil.
On flat surfaces soil is just moved around but on slopes soil is displaced downhill resulting in mass movement/ loss of soil.
On a slope, soil is splashed further downhill than uphill.
Higher Geography Applications Ed. Martin Duddin; 2006

8. Sheet Wash
Rainsplash moves soil particles that clog up soil pores and therefore reduce the amount of water that can infiltrate the soil.
Water then flows over the surface of the soil where it removes the dislodges soil.

9. Rills and Gullies
These are the most serious forms of soil erosion by water. These form where the land has slight slopes and heavy rain rushes across the surface. The rain makes its way into natural grooves and channels (made by ploughing) and gathers volume, speed and power. The water then removes soil and widens the channels.
Rills are usually not permanent and the channels can move or be ploughed over. However, the damage (loss of soils) has already been done. Water following in these rills can develop into gullies.
Gullies are steep sided channels that are permanent, gullies can form that are several meters wide and deep, these channels can erode back into the soil (similar to a river eroding) and the gullies can continue to develop.

10. Factors affecting soil erosion
There are a number of factors that affect the amount of soil erosion happening. These are:
Steepness of slope
Frequency and intensity of rainstorms
Depth and permeability of soil
Vegetation cover
Discuss with a partner how these factors would affect the amount of soil erosion and complete question 6 in your booklet (page 3 & 4).

11. Factors affecting soil erosion
Use the following information and add/ change your notes.
Steepness of slope – steeper slopes increase speed of water and therefore erosion.
Frequency and intensity of rainstorms – violent summer thunderstorms, intense rain does not have time to soak into the soils and flows over the surface.
Depth and permeability of soil – deep porous soil will absorb more water.
Vegetation cover – plants protect the soil from water erosion by slowing the water down and absorbing some of the water.

12. Soil Erosion by Wind
Wind erosion in semi-arid areas is very common. Use the diagram below to complete question 7 in your booklet.